Asynchronous Transfer Mode (ATM) technology is used as a backbone technology for some modern carrier networks. ATM supports network transmission of information including data as well as real-time voice and video. Networks employing ATM are typically characterized by a topology wherein network switches establish a logical circuit from one end of the network to another.
This topology functions to effectively guarantee Quality of Service (QoS) for the information transmitted over the ATM network. Inherent flexibility and efficiency typify ATM networks because unused bandwidth within the logical circuits therein can be appropriated when needed. For instance, idle bandwidth in an ATM circuit supporting a videoconference can be used to transfer bursts of data.
QoS specificity allows smooth ATM transmission of real-time critical information such as voice and video by providing a constant bit rate (CBR) to guarantee them sufficient bandwidth. Unspecified bit rate (UBR) provides a best effort for transmission of non-critical data. Applications that require minimal delay (e.g., interactive media), and bursty transaction traffic are respectively supported by real-time and non-real-time variable bit rate (rt-VBR and nrt-VBR).
ATM standards define the Private Network-to-Network Interface (PNNI) as the routing protocol for ATM networks. The PNNI protocol is a source routed protocol that allows network switches inform one another with data relating to the topology characterizing the network. This allows the network switches to intelligently make forwarding and other routing decisions, based on the information about the network topology. PNNI thus supports decision making for routing data traffic between a source node and a destination node through a link (or multiple links) in an ATM network.
Like the Open Shortest Path First (OSPF) protocol, an interior gateway protocol (IGP) that tries to optimize routing for Internet Protocol (IP) traffic over a Transfer Control Protocol/Internet Protocol network, upon which it is based, PNNI can route traffic in an ATM network based on cost metrics. In contrast to OSPF however, PNNI can further base routing decisions on other metrics, such as line capacities and delays, among other factors. The PNNI standard defines several metrics and attributes for selecting routing from a particular source to a particular destination, for each link to be traversed.
PNNI based metrics for selecting routing between a source and node for each link traversed can include administrative weight, which is a user configured value based on a network user's own programming. The PNNI based metrics can also include cell delay variation, which is based on the load carried by a particular link, or a statistically defined value based on link characteristics.
Such characteristics can include the speed at which the link operates and/or the buffering capability, e.g., the amount of buffer available at a node for storing the incoming data cells associated with the link. Further, the PNNI based metrics can include cell transfer delay, which can also be based on the link's load, and/or upon the characteristics of link speed and/or buffer capacity. PNNI standard based link attributes include a cell loss priority of zero (0), a cell loss priority of (0+1), a cell rate margin, and a variance factor.
These various characteristics can be affected by other attributes of the link, such as the link's basis, type, etc. For instance, the characteristics can differ between links that are satellite based and those that are terrestrial, and between encrypted links and those that are unencrypted. Some links comprise virtual trunks, with their own unique characteristics. Links that utilize public network infrastructure (e.g., facilities, lines, equipment, etc.) can differ characteristically from links that utilize private, dedicated infrastructure. These instances exemplify other link attributes that can affect indicate speed, delay, security, cost, and other link characteristics.
Users of ATM networks can prefer to route their calls and data via links of various types and basis's. Some users prefer to route calls over certain types of links and not over others and this may vary depending upon the type of call. Thus, ATM network users can attempt to manage their links and routing efficiently and/or cost effectively.
For example, in defense related (as well as certain commercial, business related, and other) networking applications, it may be specified that data traverse only encrypted links, e.g., for the heightened security they provide. Network applications, such as those that support the transfer of real time data, can be sensitive to delay and such applications may prefer to avoid satellite based links, because delay may be an unwelcome characteristic thereof, as compared to an exemplary terrestrial link.
Further, some PNNI networks operate with node policies and/or peer group (PG) policies, also known as coloring. These node and/or PG policies can provide input in making routing decisions. Node policies can be helpful in PNNI networks. For instance, a PNNI node can have multiple available PNNI links (some can have many, e.g., over 100), as well as PG policies.
Conventionally, routing through a PNNI network can be achieved on the basis of, for example, delay, cost, etc. However, routing on the basis of delay, for example, removes the capacity to route on the basis of cost.